Determining SINR in a communications system

Abstract

Diversity path signals, each comprising time division multiplexed symbols in a time slot including known symbols constituting a reference signal, are combined with respective weights to reduce co-channel interference. The weights are determined, from a correlation matrix and a reference signal correlation vector, using a sliding window starting with synchronization symbols and/or CDVCC (coded digital verification color code) symbols as the known symbols. SINR (signal to interference plus noise ratio) is determined for each window position from elements of the correlation matrix and the reference signal correlation vector. The determined SINRs are averaged through the time slot, over a plurality of time slots, and for the diversity paths to provide an accurate determination of SINR within a short period. The SINR provides a reliable signal quality parameter that is useful in a cellular communications system for procedures such as hand-off, adaptive channel allocation, dynamic power control, and cell tiering.

What is claimed is: 
     
       1. A method of determining SINR (signal to interference plus noise power ratio) in a communications system in which diversity path signals, each comprising a plurality of time division multiplexed symbols in a time slot including known symbols constituting a reference signal, are combined with respective weights to produce a combined signal for demodulation, the method comprising the steps of: determining a correlation matrix of the diversity path signals and a reference signal correlation vector; and   determining SINR from the correlation matrix and the reference signal correlation vector.   
     
     
       2. A method as claimed in claim 1 wherein the weights for combining the diversity path signals to produce the combined signal are determined from the correlation matrix and the reference signal correlation vector. 
     
     
       3. A method as claimed in claim 1 wherein the steps of determining the correlation matrix and the reference signal correlation vector and determining SINR are performed for each of a plurality of groups of known symbols in the time slot, the method further comprising the step of averaging the determined SINR for the plurality of groups of known symbols in the time slot. 
     
     
       4. A method as claimed in claim 3 and including the step of averaging the determined SINR for a plurality of time slots. 
     
     
       5. A method as claimed in claim 4 wherein the SINR is determined for each of the diversity paths, the method fuither comprising the step of averaging the determined SINRs for the diversity paths. 
     
     
       6. A method as claimed in claim 1 and including the step of averaging the determined SINRs for a plurality of time slots. 
     
     
       7. A method as claimed in claim 1 wherein the SINR is determined for each of the diversity paths, the method further comprising the step of averaging the determined SINRs for the diversity paths. 
     
     
       8. A method as claimed in claim 1 wherein, for at least one of the diversity paths, the step of determining SINR comprises determining a signal power by squaring an element of the reference signal correlation vector, determining an interference plus noise power by subtracting the determined signal power from an element of the correlation matrix representing a sum of signal, interference, and noise powers, and dividing the determined signal power by the determined interference plus noise power to deteimine the SINR. 
     
     
       9. A method as claimed in claim 1 wherein the respective weights with which the diversity path signals are combined are produced in dependence upon a respective correlation matrix and reference signal correlation vector for a plurality of positions of a window in the time slot, the method further comprising the step of determining and averaging the SINR for a plurality of the window positions in the time slot. 
     
     
       10. A method as claimed in claim 9 and including the step of averaging the determined SINR for a plurality of time slots. 
     
     
       11. A method as claimed in claim 9 wherein the SINR is determined for each of the diversity paths, the method further comprising the step of averaging the determined SINRs for the diversity paths. 
     
     
       12. A method as claimed in claim 11 and including the step of averaging the determined SINR for a plurality of time slots. 
     
     
       13. A method of determining SINR (signal to interference plus noise ratio) in a communications system in which diversity path signals are combined with respective weights, the diversity path signals each comprising a plurality of time division multiplexed symbols in a time slot, comprising the steps of: determining a correlation matrix of the diversity path signals;   determining a reference signal correlation vector using as a reference signal known and/or determined symbols in the time slot;   determining SINR for each diversity path from elements of the correlation matrix and the reference signal correlation vector; and   averaging the determined SINRs for the diversity paths.   
     
     
       14. A method as claimed in claim 13 and including the step of averaging the determined SINR for a plurality of time slots. 
     
     
       15. A method as claimed in claim 14 wherein the correlation matrix and reference signal correlation vector are determined for a plurality of positions of a window in the time slot, the method further comprising the step of determining and averaging the SINR for a plurality of the window positions in the time slot. 
     
     
       16. A method as claimed in claim 13 wherein the reference signal comprises synchronization symbols and/or CDVCC (coded digital verification colour code) symbols. 
     
     
       17. A receiver for receiving via at least two diversity paths signals each comprising a plurality of time division multiplexed symbols in a time slot including known symbols constituting a reference signal, comprising: buffers for storing symbols of the diversity path signals;   a weight calculating unit for determining weights for combining symbols of the diversity path signals from the buffers in dependence upon a correlation matrix of the diversity path signals and a reference signal correlation vector;   a signal combiner arranged to combine symbols of the diversity path signals from the buffers in accordance with the respective weights determined by the weight calculating unit to produce a combined signal; and   an SINR (signal to interference plus noise power ratio) estimator responsive to elements of the correlation matlix and the reference signal correlation vector for determining SINR of at least one of the diversity path signals.   
     
     
       18. A receiver as claimed in claim 17 wherein the SINR estimator is arranged to determine SINR for each of the diversity path signals and to average the determined SINRs. 
     
     
       19. A receiver as claimed in claim 18 wherein the SINR estimator is arranged to average the determined SINR for a plurality of time slots. 
     
     
       20. A receiver as claimed in claim 19 wherein the SINR estimator is constituted by functions of a digital signal processor.